1. Field of the Invention
This invention relates generally to reflectors and methods for making them, and particularly to dish-type electromagnetic energy antennas.
2. Background Art
The proliferation of reflectors, and particularly dish-type reflectors, in fields such as solar energy, satellite communications, microwave receivers and transmitters and the like has generated an increased demand for low cost reflectors. Prior reflectors suitable for these applications, generally of a size greater than three feet in diameter, are massive systems that are cast, spun or fiberglassed and require substantial pedestal complexes for anchoring, aiming and pointing the reflector. These systems are generally expensive because they do not lend themselves to mass production techniques and are subject to extremely high shipping costs.
While conventional plastic forming techniques are gaining increasing acceptance, such techniques, including thermoforming techiques, have not gained acceptance in the field of electromagnetic energy reflectors because of the high degree of precision and strength required for these surfaces. The conventional techniques for making thermoformed plastic radio-frequency reflective surfaces have relied upon embedded metals in the plastic rather than metal films. Embedded metals in sufficient concentrations to reflect RF energy, however, weaken plastics. Additionally, because these embedded metals are mixed throughout the plastic sheet, reflection is a function of the sheet thickness and not the surface of the formed part. The surface deviation (RMS) of embedded metals can be no better than the thickness of the plastic sheet or substrate, plus any other shape deformity. If the plastic substrates are made sufficiently thin, problems develop during the metallization process due to the tendency of the substrates to deflect during metallization. Additionally, such substrates are not amenable to large scale outdoor applications because of their tendency to deflect under their own weight and to distort in response to wind loading. Discrete thin metal films, on the other hand, vary only with variations of the molded surfaces and thus lower RMS figures can be achieved.